(1) Field of the Invention
This invention relates to variable wide band fiber optic delay lines which provide a variable delay for electronic signals with with very wide bandwidth. The invention permits discrete step adjustment of the delay provided by such a delay line.
(2) Description of the Prior Art
Delay lines have found many uses in electronic processing. Their use is particularly prevalent in radar and electronic warfare or surveillance equipment. The most common delay line technology is Surface Acoustic Wave (SAW) devices. SAW devices are limited in their frequency, bandwidth and available delay. Wide band fiber optics have been proposed, as in microwave delay lines. These provide higher frequences (up to 20 gigahertz((GHz)) or more), high bandwidths (over 10 GHz), and long delays (40 kilometers of fiber give about 200 microseconds of delay, which would require 60 cm of SAW propagation).
To date, one drawback of fiber delay lines is that tunable delay is not available as in SAW technology. Delay is simply determined by the length of the fiber between transmitter and detector. Schemes that would use fiber switching are excessively complicated. Schemes that would use multiple fiber delay lines are expensive due to the expense of multiple transmitters and receivers.